when I migrated from 2.0.23 to 2.1.14 I got errors when importing my
data. This was due to the schemachecking, apparently only one toplevel
structural objectclass was allowed. I've read the rfc 2252 however, and
I can't figure out why this restriction was imposed.

This discussion has probably been done before the release of the 2.1.x,
but I can't seem to find a trace of it. Can anyone direct me to a
document of some sort that motivates this decision ?